Conventional Solid State Drives (SSDs) have used Redundant Array of Inexpensive Drives (RAID)-like redundancy to provide results similar to conventional hard disk drives (HDDs) to recover from certain types of errors. Such redundancy has typically been implemented as “1 die out of n” so that an entire NAND die is consumed by the redundancy. In an 8 NAND die, one of the NAND die is used for RAID-5-like redundancy, reducing capacity by ⅛th, but providing protection against various types of errors.
One issue with redundancy in a SSD is the overall capacity of the drive. Consumers want as much drive space to be available for data as possible. A SSD is normally manufactured with some type of over provisioning, which is the difference between the actual capacity and the advertized capacity. The over provisioning should be kept as low as possible to maintain competitive prices for each unit of available storage.
It would be desirable to reduce over provisioning when protecting user data using a RAID-like redundancy scheme where redundancy information is stored in a location separate from the user data being protected.